Evaporation loss control

ABSTRACT

In a system for controlling the loss of fuel vapor from a vehicle fuel tank, the fuel tank vents are connected to the upper portion of a canister containing a quantity of fuel vapor adsorbing carbon retained under compression therein. The upper portion of the canister is also connected to the induction system of the vehicle engine, the bottom of the canister being open to atmosphere so that air is drawn through the carbon and the fuel vapor purged during engine operation. The canister is molded from nylon, the top being formed so that vapor from the fuel tank is discharged into the mid-portion of the canister. The top and bottom of the canister include molded grids and filter pads to prevent loss of carbon from the canister, and in one embodiment a nylon screen additionally serves to prevent carbon loss from the bottom of the canister. The top of the canister may contain appropriate valve structure to control fuel tank pressure and vapor flow.

United States Patent; [15] 3,683,597 Beveridge et al. 51 Aug. 15, 1972[54] EVAPORATION LOSS CONTROL FOREIGN PATENTS OR APPLICATIONS [7Inventors: m m s p gzn 545,089 5/1942 Great Britain ..55 s13 r e ster, to Primary Examiner-Dennis E. Talbert, Jr. [73] Assigneez General MotorsCorporation Attorney-J. L. Carpenter and C. K. Veenstra Detroit, Mich. 1ABS CT [22] Filed: Sept. 17', 1970 In a system for controlling the lossof fuel vapor from p 73,128 a vehicle fuel tank, the fuel tank vents areconnected Related us. Application Data to the upper portion of: acanister containing a quantity of fuel vapor adsorbmg carbon retainedunder com- 1 Continuation-Imp?!" 0f 837,868, pression therein. The upperportion of the canister is I969, abandonedalso connected to theinduction system of the vehicle engine, the bottom of the canister beingopen to at- [52] US. Cl. ..55/3l6, 55/387, 55/419, mosphere so that i isdrawn through the carbon and 55/476, 55/513, 55/518 55/519 SS/DIG- thefuel vapor purged during engine operation. The 123/119 123/136 canisteris molded from nylon, the top being formed [51] III. CI. ..B0ld 50/00 sothat vapor from the f tank i discharged into the [58] Fleld of Search..-.55/3 16, 387, 419, 420, 476, mid ponion of the Canister The top andbottom of the 55/512 canister include molded grids and filter pads to1310- 28; 123/1 119 119 136 prevent loss of carbon from the canister,and in one embodiment a nylon screen additionally serves to [56]References cued prevent carbon loss from the bottom of the canister.UNITED STATES PATENTS The top of the canister may contain appropriatevalve 2 586 672 2/1952 Lambensen 55/387 structure to control fuel tankpressure and vapor flow. 3:19 1 :587 6/1965 Hall 123/136 13 Claims, 15Drawing Figures 1% 25 26 V w Pt 11 a: 12 e 25 f1 5 Patented Aug. 15,1972 4 Sheets-Sheet l y m'vavroR flamas 1?; Bauer ATTORNEY Patented Aug.15, 1972 3,683,597

4 Sheets-Sheet 2 INVEXTORS fiomas A. Bereriayefi BY 172.51% A. fianfzfATTORNEY Patented Aug. 15, 1972 3,683,597

4 Sheets-Sheet 5 I NVENTORS flames K. Bever/age, 6 BY 1725i K. Ran/zZJKMW ATTORNEY SUMMARY OF THE INVENTION In one of the systems found tobe most advantageous for controlling loss of fuel vapor from vehiclefuel tanks, a canister containing activated charcoal is connected to thefuel tank vents and stores the fuel vapor emitted therefrom. Duringvehicle operation, the fuel vapor is purged from the canister into theengine induction system.

I This invention provides a canister having a construction particularlysuited for use in such a system.

The details as well as other objects and advantages of this inventionare shown in the drawings and are set forth in the detailed descriptionof the preferred embodiment.

SUMMARY OF THE DRAWINGS FIG. 1 is a schematic diagram of a systememploying the canister in the manner described;

FIG. 2 is an enlarged sectional view of the canister in elevation, takenalong line 2-2 of FIG. 3, showing the construction of the canisterassembly;

FIG. 3 is a plan view of the canister, taken in section along line 3-3of FIG. 2, showing the inlet and purge fittings of the canister;

FIG. 4 is a plan view of the upper portion of the canister body member,indicated generally by line 4-4 of FIG. 2, the cover member of thecanister assembly having been removed to show the top grid structure;

FIG. 5 is a sectional view taken along line 5-5 of FIG. 4, furtherenlarged to show details of the top grid structure;

FIG 6 is a plan view of the bottom closure of the canister, removed fromthe canister assembly but indicated generally by line 6-6 of FIG. 2,showing the nylon screen and bottom grid structure;

FIG. 7 is a sectional view taken along line 7-7 of FIG. 6, furtherenlarged to show the bottom grid structure, the sealing lip, and thenylon screen;

FIG. 8 is a pictorial view of the wave spring which biases the bottomclosure against the carbon in the canister; FIG. 9 is a plan view of thespring seat and filter retainer disposed at the base of the canister,removed from the canister assembly but indicated generally by line 9-9of FIG. 2;

FIG. 10 is a schematic diagram of another system employing the featuresof the canister shown in FIG. 2;

FIG. 10a is a schematic plan view of the canister shown in FIG. 10,indicating how the views of FIGS. 1 l, 12 and 13 are taken;

FIG. 11 is an enlarged sectional view of the top portion of thecanister, taken generally along line 11-11 of FIG. 10a, showing thepressure and vacuum control valves disposed in the cover member;

FIG. 12 is a sectional view taken along line 12-12 of FIG. 10a showingone purge fitting;

FIG. 13 is a sectional view taken along line 13-13 of FIG. 10a showingthe second purge fitting;

FIG. .14 is a schematic diagram of an additional system employing acanister with similar features; and

FIG. 15 is an enlarged axial sectional view of the canister shown inFIG. 14, illustrating the purge control valve disposed in the covermember and also illustrating an improved arrangement of polyurethanefoam pads which retain the charcoal in the canister.

DETAILED DESCRIPTION OF THE PREFERRED ODIMENT Referring first to thesystem of FIG. 1, a vehicle fuel tank or reservoir 10 has a plurality ofvent lines 11 and 12 extending to a liquid-vapor separator 13. Fuelvapor emitted from tank 10 passes through vent lines 11,12, separator13, and a vent line 14 and is received by a fitting 15 (FIG. 3) of acanister assembly 16. Canister 16 contains an adsorbent which stores thefuel vapor therein. Another fitting 17 (FIG. 3) on canister 16 isconnected through a purge line 18 to the engine induction passage 19 ata port 20 disposed below the throttle 21. Air flow is thereby inducedthrough the canister during engine operation to purge the fuel vaporfrom the adsorbent. As shown in FIG. 3, fitting 17 contains arestricting orifice 22 whereby the flow through purge line 18 ismaintained at a low rate. Another fitting 23 (FIG. 3) on canister 16 isconnected through a purge line 24 to the snorkel 25 of the engine aircleaner 26; additional purge air flow is thereby induced throughcanister 16 by the varying vacuum conditions which are created asinduction air flows through snorkel 25.

As may be seen in FIG. 2, the body portion of canister 16, molded fromheat stabilized nylon, has a generally cylindrical side wall 2 and anupper end wall comprising an annular outer portion 28 and an innerportion 29 connected by a concentrically disposed, upwardly opening,generally frusto-conical or cylindrical inner wall 30. A sealing lip 31extends upwardly around the perimeter of annular portion 28.

As may be seen in figs. 4 and 5, outer wall 28 is formed in a gn'ddedstructure having a plurality of flat ribs 32 extending radially frominner wall 30 to sealing lip 31 and spaced circumferentially about innerwall 30 and a plurality of undulating ribs 33 also extending radiallyfrom inner wall 30 to sealing lip 31 between flat ribs 32 with acircumferential dimension substantially equal to the circumferentialspacing between fiat ribs 32. The peak portions 34 of undulating ribs 33are disposed at the same height as flat ribs 32, and the valley portions35 of undulating ribs 33 are disposed lower than flat ribs 32. Aplurality of circular ribs 36 are spaced between inner wall 30 and outerwall 31 and interconnect peak portions 34 of undulating ribs 33 withflat ribs 32. The grid formed by flat ribs 32, undulating ribs 33, andcircular ribs 36 defines a plurality of apertures 37 (FIG. 5) which openhorizontally from spaces above the valley portions 35 of undulating ribs33 and between circular ribs 36 to spaces below flat ribs 32 and betweencircular ribs 36.

Inner wall 29 has a similar grid structure comprised of flat ribs 38,undulating ribs 39, and cross ribs which interconnect the peak portionsof undulating ribs 39 with flat ribs 38. A separate sectional view ofthe grid structure for inner wall 29 is not presented since its features are adequately shown in the grid illustration of FIGS.

A cover member 40, molded of heat stabilized nylon, is secured to innerwall 30 and sealing lip 31. Cover member 40 includes fittings 15, 17,and 23 and a depending cylindrical wall 41 extending within inner wall30. Depending wall 41 has a plurality of ribs 42 which retain apolyurethane filter pad 43 against inner gridded wall 29 within thechamber defined by gridded wall 29, inner wall 30, and cover member 40.An annular polyurethane filter pad 44 is retained within the chamberdefined by cover member 40, annular gridded wall 28, inner wall 30, andsealing lip 31.

The chamber 45 formed within canister assembly 16 contains a quantity ofactivated charcoal or carbon 46 which has the property of adsorbing fuelvapor. Charcoal 46 is maintained within canister assembly 16 in atightly packed condition by a lower wall or closure member 47 and a fineme'sh nylon screen 48, both shown and described below in greater detailthe reference to FIGS. 6 and 7. Lower wall 47 has an upward bias appliedby a wave spring 49 shown in FIG. 8. A base member 50, molded from heatstabilized nylon and secured to the lower end of side wall 27, has anannular shoulder 51 extending inwardly from side wall 27 which defines acentral opening 52 bisected by a bar 53. Shoulder 51 supports wavespring 49 and, in conjunction with bar 53, also supports a polyurethanefilter pad 54 which filters air entering the base of the canister.

As shown in greater detail in FIGS. 6 and 7, lower wall member 47, alsomolded from heat stabilized nylon, has a gridded structure comprising aplurality of circular ribs 55 and a plurality of radially extending ribs56. As may be seen in FIG. 7, the base 57 of radial ribs 56 is fiatwhile the upper surface 58 of ribs 56 has an undulating form in whichthe peak portions 59 are disposed intermediate circular ribs 55 and thevalley portions 60 occur at circular ribs 55.

A sealing lip 61 formed on lower wall member 47 is resiliently biasedoutwardly to engage outer wall 27 as shown in FIG. 2.

FIG. 10 shows another system utilizing the features of canister 16. Thesame reference numerals are used to designate the same components ineach system. Referring to FIG. 10, a vehicle fuel tank 10 has aplurality of vent lines 11,12 which extend to a liquid-vapor separator13. A vent line 14 directs fuel vapor from separator 13 to a fitting 62(FIG. 11) of a canister assembly 63 which contains a fuel vaporadsorbent. Another fitting 64 (FIG. 12) on canister 63 has a purge line18 extending to the engine induction passage 19 at a location 20 belowthe throttle 21. Air flow is thereby induced through the canister duringengine operation to purge the fuel vapor from the adsorbent. Anadditional fitting 65 (FIG. 13) on canister 63 has a purge line 66extending to induction passage 19 at a port 67; port 67 is locatedupstream of throttle 21 when throttle 21 is closed and is traversed bythrottle 21 as throttle 21 is opened. Port 67 is thereby subjected tothe vacuum conditions below throttle 21 during open throttle operationand induces an additional purge air flow through canister 63 during openthrottle operation.

A valve structure indicated generally by 68 connects the carburetor fuelbowl 69 with the engine air cleaner 26 on the clean side of the filterelement 70 during engine operation and connects carburetor fuel bowl 69through a vent line 71 to purge line 66 when the engine is notoperating; thus fuel vapors formed in fuel bowl 69 when the engine isnot operating are vented through lines 71 and 66 to canister 63. Thebody and lower portions of canister assembly 63 are identical to thoseof canister assembly 16; only the cover members difier.

Referring to FIGS. 11, 12 and 13, the cover member 72 for canister 63sealingly engages inner wall 30 and sealing lip 31 and has a dependingwall 41 provided with ribs 42. A passage 73 extending through fitting 62opens into a chamber 74 beneath a diaphragm type valve member 75. Asfuel vapor pressure in tank 10, vent line 14, passage 73 and chamber 74increases, valve member 75 is raised against the bias of its spring 76so that fuel vapor may flow through valve seat 77 to the charcoal 46.

An umbrella valve member 78 responds to a predetermined reduction inpressure in tank 10, vent line 14, passage 73, and chamber 74, openingto permit air flow through a polyurethane filter pad 79 and a pluralityof orifices 80 to chamber 74 and thus through passage 73 and vent line14 to tank 10.

FIG. 14 shows an additional system utilizing a canister similar tocanister 16. The same reference numerals are used to designate the samecomponents in each system. Referring to FIG. 14, a vehicle fuel tank 10has a plurality of vent lines 11,12 which extend to a liquid-vaporseparator 13. A vent line 14 directs fuel vapor from separator 13 to afitting 81 of a canister assembly 82 which contains a fuel vaporadsorbent. Another fitting 83 has a purge line 18 extending to theengine induction passage 19 at a location 20 below the throttle 21. Anadditional fitting 84 has a vacuum signal line 85 extending to inductionpassage 19 at a port 67 located upstream of throttle 21 when throttle 21is closed and traversed by throttle 21 as throttle 21 is opened; port 67is thereby subjected to the vacuum conditions below throttle 21 duringopen throttle operation.

A valve structure indicated generally by 86 is opened through linkage(not shown) from throttle 21 whenever throttle 21 is closed; fuel vaporsformed in fuel bowl 69 are then vented through a vapor line 87 to afitting 88 on canister 82.

The body portion of canister 82 is identical to the body portion ofcanister 16 and will not be described further. A body of fuel vaporadsorbing charcoal 46 is retained in canister 82 between a centralpolyurethane filter pad 89 and an annular polyurethane filter pad 90,both at the top of canister 82, and a polyurethane filter pad 91 at thebottom of canister 82. During assembly, the gridded lower wall orclosure member 47, identical to that used in canister 16, squeezescharcoal 46 and polyurethane pads 89, 9t) and 91 to tightly pack thecharcoal and compress the polyurethane pads. Lower wall 47 is thensecured in place, and any subsequent tendency of charcoal 46 to compactis compensated by expansion of polyurethane pads 89, and 91. Charcoal 46is thus maintained in a tightly packed condition without the wave spring49 used in canister 16. A base member 50, identical to that used incanister 16, supports a fiberglass pad 92 which filters air entering thebase of the canister.

A cover member 93, molded of heat stabilized nylon, is secured to theinner wall 30 and the sealing lip 31 at the top of the canister body.Cover member 93 includes fittings 81, 83, 84, and 89 and has a dependingwall 41 extending within inner wall 31). A plurality of ribs 42,extending inwardly from wall 41, retain a polyurethane filter pad 43against the inner gridded wall 29 within the chamber defined by griddedwall 29, inner wall 30, and cover member 93.

Cover member 93 includes a purge control unit to which lines 18 and 85are connected through fittings 83 and 84 respectively. Under closedthrottle conditions of operation, manifold vacuum is applied throughline 18 to a chamber 94 below a diaphragm 95. This inthrees a flow ofair into the base of canister 82 and through filter 92, charcoal 46,central gridded wall 29, and a restriction 96. This air flow purgesadsorbed fuel vapor from charcoal 46 and delivers it through purge line18 to induction passage 19 for combustion in the engine. Restriction 96maintains this flow at a low rate.

During closed throttle operation, the vacuum in chamber 94 pullsdiaphragm 95 downwardly against a spring 97, and a valve 98 formed as aportion of diaphragm 95 engages an annular valve seat 99. When throttle21 is opened, port 67 senses the vacuum therebelow and applies thisvacuum through vacuum signal line 85 to a chamber 109 above diaphragm95. The pressures on opposite sides of diaphragm 95 are therebyequalized, and spring 97 lifts valve 99 away from seat 99. The vacuum inchamber 94 then induces an additional purge air flow into the base ofcanister 82 and through filter 92, charcoal 46, annular gridded wall 28,and a restriction 101.

OPERATION It will be noted that, in each embodiment, fuel vapor emittedfrom tank enters the canister through inner gridded wall 29 near themid-portion of the canister, at a location axially removed from annulargridded wall 28. The vapor is dispersed downwardly through charcoal 46both by gravitational force and by the difference between the fuel vaporpressure and the atmospheric pressure ambient the lower end of thecanister. Moreover, in each embodiment, purge vacuum created duringengine operation is applied through annular gridded wall 28 and drawsair through the lower filter pad and charcoal 46, thus purging fuelvapor from charcoal 46. The quantity of charcoal 46 located in theannulus about inner wall 31) smoothes the flow of fuel vapor in thepurge air stream. The lower filter pads 54 or 92 prevent dust fromentering charcoal 46 and, in conjunction with nylon screen 49 orpolyurethane pad 91 and the grid structure of lower wall member 47, alsoprevents carbon particles from dropping out of the canister assembly.The annular polyurethane pads 44 or 90, in conjunction with annulargridded wall 28, prevent carbon particles from being drawn into theengine induction system.

Also during engine operation, engine vacuum applied from port 20 throughfittings 17, 64, or 83 purges fuel vapor directly from fuel tank 19through vent line 14 and purges fuel vapor from charcoal 46 by drawingair through the lower filter pads 54 or 91) and charcoal 46. Thepolyurethane pads 43 and 89, in conjunction with inner gridded wall 29,also prevent carbon particles from being drawn into the inductionsystem.

Construction of the canister assembly with the fuel vapor inlet andpurge fittings at the top and the atmospheric opening at the bottom notonly permits ready dispersion of fuel vapor through the charcoal butadditionally pemrits discharge of any fuel that may be unexpectedlydelivered to the canister assembly beyond the storage capacity of thecharcoal. Fuel discharged from the bottom of the canister may be ductedto a remote location in some circumstances.

It will be appreciated that other systems may utilize the features ofthe canister described above; in the FIG. 2 embodiment, for example, thepurge flow provided by vent line 18 is unnecessary in some systems andfitting 17 is then plugged or eliminated entirely.

We Claim:

1. A canister for use in a system for controlling loss of fuel vaporfrom a vehicle having a fuel reservoir and an internal combustion enginewith an induction passage, said canister comprising means forming agenerally cylindrical side wall and a pair of oppositely disposed endwalls which define a chamber therewithin,

one of said end walls having a central portion and an outer annularportion with said central portion disposed closer to the other of saidend walls than said outer portion and connected to said outer portion bya generally cylindrical portion,

a quantity of fuel vapor adsorbing material filling said chamber, fuelvapor inlet means connected to said central portion and adapted forconnection to said reservoir whereby fuel vapor emitted from saidreservoir may be dispersed into said adsorbing material from amid-portion thereof,

and fuel vapor outlet means connected to said outer portion and adaptedfor connection to said induction passage whereby fuel vapor may bepurged from said adsorbing material to said induction passage through anarea surrounding said midportion and axially removed therefrom.

2. The canister of claim 1 which further comprises additional fuel vaporoutlet means connected to said central portion and adapted forconnection to said induction passage whereby fuel vapor also may bepurged from said mid-portion of said adsorbing material to saidinduction passage and directly from said reservoir to said inductionpassage.

3. The canister of claim 1 wherein said end walls are molded from aplastic material and comprise grids permitting fluid flow to and fromsaid adsorbing material but preventing loss of said adsorbing materialform said chamber.

4. The canister of claim 3 which further comprises filter meansoverlying said grids for preventing entrance of dust to said chamber andloss of said adsorbing material from said chamber.

5. A canister for use in a system for controlling loss of fuel vaporfrom a vehicle having a fuel reservoir and an internal combustion enginewith an induction passage, said canister comprising a molded plasticbody member having a generally cylindrical side wall with a verticalaxis, an annular end wall intersecting said side wall at its upper endand extending inwardly therefrom, said end wall being molded in a griddefining a plurality of apertures extending therethrough, said end wallhaving an upwardly extending sealing lip circumscribing said grid, anupwardly opening generally frustoconical inner wall disposedconcentrically about said axis and intersecting said end wall andextending upwardly and downwardly therefrom, and an inner grid disposedat the lower end of said inner wall, said inner grid defining aplurality of apertures extending therethrough,

a quantity of fuel vapor adsorbing material contained in the portion ofsaid body member immediately below said annular end wall grid and saidinner grid and surrounding the portion of said inner wall below said endwall,

and a molded plastic cover member secured over said body member andengaging said sealing lip and said inner wall to define an annularchamber above said annular end wall grid and an inner chamber above saidinner grid, said cover member having an inlet fitting opening to saidinner chamber and adapted for connection to said fuel reservoir and apurge fitting opening from said annular chamber and adapted forconnection to said induction system whereby fuel vapor emitted from saidreservoir may be dispersed into said adsorbing material from amid-portion thereof and whereby fuel vapor may be purged from saidadsorbing material to said induction system through an area surroundingsaid midportion and axially removed therefrom.

6. The canister of claim wherein said body member and said cover memberare molded from heat stabilized nylon.

7. The canister of claim 5 wherein said annular end wall grid is formedby a plurality of flat ribs extending radially from said inner wall tosaid sealing lip and spaced circumferentially about said inner wall, aplurality of undulating ribs also extending radially from said innerwall to said sealing lip between said flat ribs and having acircumferential dimension substantially equal to the circumferentialspacing between said flat ribs, said undulating ribs having peakportions disposed at the same height as said flat ribs and valleyportions disposed lower than said flat ribs, and a plurality of circularribs spaced between said inner wall and said sealing lip andinterconnecting said peak portions of said undulating ribs with saidflat ribs, whereby said apertures extending through said end wall gridare defined to open horizontally from spaces above said valley portionsand between said circular ribs to spaces below said flat ribs andbetween said circular ribs.

8. The canister of claim 5 wherein said inner wall grid is defined by aplurality of spaced parallel flat ribs, a plurality of parallelundulating ribs disposed between said flat ribs and having a widthsubstantially equal to the spacing between said flat ribs, saidundulating ribs having peak portions disposed at the same height as saidflat ribs and valley portions disposed lower than said flat ribs, and aplurality of cross ribs extending perpendicular to said flat andundulating ribs and interconnecting said peak portions of saidundulating ribs with said flat ribs, whereby said apertures extendingthrough said inner wall grid are defined to open horizontally fromspaces above said valley portions and between said cross ribs to spacesbelow said flat ribs and between said cross ribs.

9. A canister for use in a system for controlling loss of fuel vaporfrom a fuel reservoir, said canister comprising means fomiing agenerally cylindrical side wall and an end wall which define a chamberopen at one end,

fuel vapor inlet means opening into said chamber and adapted forconnection to said reservoir whereby fuel vapor emitted from saidreservoir may be conducted to said chamber,

a quantity of fuel vapor adsorbing material disposed within saidchamber,

means forming a closure disposed adjacent said open end of said chamberand having its circumference slidably engaging said side wall,

and spring means biasing said closure forming means toward said end wallwhereby said adsorbing material is retained in a tightly packed mannertherebetween.

10. The canister of claim 9 which further comprises an annular springseat portion extending inwardly from said side wall at said open end ofsaid chamber and overlapping said circumference of said closure formingmeans, and wherein said spring means comprises a wave spring disposedbetween said spring seat portion and said closure forming means.

ll 1. A canister for use in a system for controlling loss of fuel vaporfrom a fuel reservoir, said canister comprising means fomiing agenerally cylindrical side wall and an end wall which define a chamberopen at one end,

fuel vapor inlet means opening into said chamber and adapted forconnection to said reservoir whereby fuel vapor emitted from saidreservoir may be conducted to said chamber,

a quantity of fuel vapor adsorbing material disposed within saidchamber,

means forming a closure disposed adjacent said open end of said chamber,

and compressed polyurethane pads disposed between said adsorbingmaterial and said end wall and said closure to retain said adsorbingmaterial in a tightly packed manner therebetween.

12. A canister for use in a system for controlling loss of fuel vaporfrom a vehicle having a fuel reservoir and an internal combustion enginewith an induction passage, said canister comprising a molded plasticbody member having a generally cylindrical side wall with a verticalaxis, an annular end wall intersecting said side wall at its upper endand extending inwardly therefrom, said end wall being molded in a griddefining a plurality of apertures extending therethrough, said end wallhaving an upwardly extending sealing lip circumscribing said grid, anupwardly opening generally frustoconical inner wall disposedconcentrically about said axis and intersecting said end wall andextending upwardly and downwardly therefrom, and an inner grid disposedat the lower end of said inner wall, said inner grid defining aplurality of apertures extending therethrough,

an annular polyurethane filter pad overlying said annular end wall grid,

an inner polyurethane filter pad overlying said inner a molded plasticcover member secured over said body member and engaging said sealing lipand said inner wall to define an annular chamber containing said annularfilter pad and an inner conical inner wall disposed concentrically aboutsaid axis and intersecting said end wall and extend ing upwardly anddownwardly therefrom, and an inner grid disposed at the lower end ofsaid inner chamber containing said inner filter pad, said wall, saidinner grid defining a plurality of apercover member having an inletfitting opening to tures extending therethrough, said inner chamber andadapted for connection to a molded plastic cover member secured oversaid said fuel reservoir and a purge fitting opening from body memberand engaging said sealing lip and said annular chamber and adapted forconnection said inner wall to define an annular chamber above to saidinduction system, 10 said annular end wall grid and an inner chamber aquantity of fuel vapor adsorbing material contained above said innergrid, said cover member having in the portion of said body memberimmediately an inlet fitting opening to said inner chamber and belowsaid annular end wall grid and said inner adapted for connection to saidfuel reservoir and a grid and surrounding the portion of said inner wallpurge fitting opening from said annular chamber below said end wall, andadapted fro connection to said induction a 2 5 nylon Screen underlying'sald adsorbmg a of fuel vapor adsorbing material contained a moldedplastic lower wall member underlying and m the Porno of P body P P belPwSald supporting said screen and said adsorbing materiwan 1 and End andf' 4 al, said lower wall member being molded in a grid mundmg the Pornoof sad wan below defining a plurality of apertures therethrough, saidend wall lower wall member having a depending skirt a molded plasticlower wall member underlying and biased into engagement with said sidewall, Suppomng adsmbmg, F lower f alower filter pad underlying saidlower wall member member, F to slde Y and bemg grid, molded in a griddefining a plurality of apertures a molded plastic base member securedto the lower therethrough,

end of said side wall, said base member having an a Pompressed mule}:polyurethane P annular shoulder extending inwardly from said beftween lannular end wall gnd and side wall and defining a central opening andhaving sald adsorbmg mammal a bar extending diametrically across saidopening a compressed, 3 y filter f dlsposefi to divide said opening intotwo portions, Said between said inner grid and said adsorbingmaterishoulder and said bar supporting said lower filter pad, acompressed lower polyurethane pad disposed and a wave spring memberSupported on Said between said adsorbing material and said lowershoulder and biasing said lower wall member upwall wardly against saidadsorbing material to retain the E F of Said pPlyufethanePads retammgsaid material in a tightly packed condition. adsorbmg mammal m a t'ghtlyPacked 13. A canister for use in a system for controlling loss i of fuelvapor from a vehicle having a fuel reservoir and an i filter Padunderlymg 531d lower wall member an internal combustion engine with aninduction 40 passage said canister comprising and a molded plastic basemember secured to the a molded plastic body member having a generallylower end of said side wall, said base member havcylindrical side wallwith a vertical axis, an annular g annular shoulder, extendmg inwardlyfrom end wall intersecting said side wall at its upper end Slde wall andf g a cerltral opemng l and extending inwardly therefrom, said end wallhavulg a e xtend mg dlamemcany across sald being molded in a griddefining a plurality of aperoPenmg to dmde opemng P "9 P9 turesextending therethrough, said end wall having sald shoulder and Sald barsupporting sald filter an upwardly extending sealing lip circurnscribingsaid grid, an upwardly opening generally frusto-

1. A canister for use in a system for controlling loss of fuel vaporfrom a vehicle having a fuel reservoir and an internal combustion enginewith an induction passage, said canister comprising means forming agenerally cylindrical side wall and a pair of oppositely disposed endwalls which define a chamber therewithin, one of said end walls having acentral portion and an outer annular portion with said central portiondisposed closer to the other of said end walls than said outer portionand connected to said outer portion by a generally cylindrical portion,a quantity of fuel vapor adsorbing material filling said chamber, fuelvapor inlet means connected to said central portion and adapted forconnection to said reservoir whereby fuel vapor emitted from saidreservoir may be dispersed into said adsorbing material from amid-portion thereof, and fuel vapor outlet means connected to said outerportion and adapted for connection to said induction passage wherebyfuel vapor may be purged from said adsorbing material to said inductionpassage through an area surrounding said midportion and axially removedtherefrom.
 2. The canister of claim 1 which further comprises additionalfuel vapor outlet means connected to said central portion and adaptedFor connection to said induction passage whereby fuel vapor also may bepurged from said mid-portion of said adsorbing material to saidinduction passage and directly from said reservoir to said inductionpassage.
 3. The canister of claim 1 wherein said end walls are moldedfrom a plastic material and comprise grids permitting fluid flow to andfrom said adsorbing material but preventing loss of said adsorbingmaterial form said chamber.
 4. The canister of claim 3 which furthercomprises filter means overlying said grids for preventing entrance ofdust to said chamber and loss of said adsorbing material from saidchamber.
 5. A canister for use in a system for controlling loss of fuelvapor from a vehicle having a fuel reservoir and an internal combustionengine with an induction passage, said canister comprising a moldedplastic body member having a generally cylindrical side wall with avertical axis, an annular end wall intersecting said side wall at itsupper end and extending inwardly therefrom, said end wall being moldedin a grid defining a plurality of apertures extending therethrough, saidend wall having an upwardly extending sealing lip circumscribing saidgrid, an upwardly opening generally frusto-conical inner wall disposedconcentrically about said axis and intersecting said end wall andextending upwardly and downwardly therefrom, and an inner grid disposedat the lower end of said inner wall, said inner grid defining aplurality of apertures extending therethrough, a quantity of fuel vaporadsorbing material contained in the portion of said body memberimmediately below said annular end wall grid and said inner grid andsurrounding the portion of said inner wall below said end wall, and amolded plastic cover member secured over said body member and engagingsaid sealing lip and said inner wall to define an annular chamber abovesaid annular end wall grid and an inner chamber above said inner grid,said cover member having an inlet fitting opening to said inner chamberand adapted for connection to said fuel reservoir and a purge fittingopening from said annular chamber and adapted for connection to saidinduction system whereby fuel vapor emitted from said reservoir may bedispersed into said adsorbing material from a mid-portion thereof andwhereby fuel vapor may be purged from said adsorbing material to saidinduction system through an area surrounding said midportion and axiallyremoved therefrom.
 6. The canister of claim 5 wherein said body memberand said cover member are molded from heat stabilized nylon.
 7. Thecanister of claim 5 wherein said annular end wall grid is formed by aplurality of flat ribs extending radially from said inner wall to saidsealing lip and spaced circumferentially about said inner wall, aplurality of undulating ribs also extending radially from said innerwall to said sealing lip between said flat ribs and having acircumferential dimension substantially equal to the circumferentialspacing between said flat ribs, said undulating ribs having peakportions disposed at the same height as said flat ribs and valleyportions disposed lower than said flat ribs, and a plurality of circularribs spaced between said inner wall and said sealing lip andinterconnecting said peak portions of said undulating ribs with saidflat ribs, whereby said apertures extending through said end wall gridare defined to open horizontally from spaces above said valley portionsand between said circular ribs to spaces below said flat ribs andbetween said circular ribs.
 8. The canister of claim 5 wherein saidinner wall grid is defined by a plurality of spaced parallel flat ribs,a plurality of parallel undulating ribs disposed between said flat ribsand having a width substantially equal to the spacing between said flatribs, said undulating ribs having peak portions disposed at the sameheight as said flat ribs and valley portions disposed lower than saidflat ribs, and a plurality of cross ribs extending perpendicular to saidflat and undulating ribs and interconnecting said peak portions of saidundulating ribs with said flat ribs, whereby said apertures extendingthrough said inner wall grid are defined to open horizontally fromspaces above said valley portions and between said cross ribs to spacesbelow said flat ribs and between said cross ribs.
 9. A canister for usein a system for controlling loss of fuel vapor from a fuel reservoir,said canister comprising means forming a generally cylindrical side walland an end wall which define a chamber open at one end, fuel vapor inletmeans opening into said chamber and adapted for connection to saidreservoir whereby fuel vapor emitted from said reservoir may beconducted to said chamber, a quantity of fuel vapor adsorbing materialdisposed within said chamber, means forming a closure disposed adjacentsaid open end of said chamber and having its circumference slidablyengaging said side wall, and spring means biasing said closure formingmeans toward said end wall whereby said adsorbing material is retainedin a tightly packed manner therebetween.
 10. The canister of claim 9which further comprises an annular spring seat portion extendinginwardly from said side wall at said open end of said chamber andoverlapping said circumference of said closure forming means, andwherein said spring means comprises a wave spring disposed between saidspring seat portion and said closure forming means.
 11. A canister foruse in a system for controlling loss of fuel vapor from a fuelreservoir, said canister comprising means forming a generallycylindrical side wall and an end wall which define a chamber open at oneend, fuel vapor inlet means opening into said chamber and adapted forconnection to said reservoir whereby fuel vapor emitted from saidreservoir may be conducted to said chamber, a quantity of fuel vaporadsorbing material disposed within said chamber, means forming a closuredisposed adjacent said open end of said chamber, and compressedpolyurethane pads disposed between said adsorbing material and said endwall and said closure to retain said adsorbing material in a tightlypacked manner therebetween.
 12. A canister for use in a system forcontrolling loss of fuel vapor from a vehicle having a fuel reservoirand an internal combustion engine with an induction passage, saidcanister comprising a molded plastic body member having a generallycylindrical side wall with a vertical axis, an annular end wallintersecting said side wall at its upper end and extending inwardlytherefrom, said end wall being molded in a grid defining a plurality ofapertures extending therethrough, said end wall having an upwardlyextending sealing lip circumscribing said grid, an upwardly openinggenerally frusto-conical inner wall disposed concentrically about saidaxis and intersecting said end wall and extending upwardly anddownwardly therefrom, and an inner grid disposed at the lower end ofsaid inner wall, said inner grid defining a plurality of aperturesextending therethrough, an annular polyurethane filter pad overlyingsaid annular end wall grid, an inner polyurethane filter pad overlyingsaid inner grid, a molded plastic cover member secured over said bodymember and engaging said sealing lip and said inner wall to define anannular chamber containing said annular filter pad and an inner chambercontaining said inner filter pad, said cover member having an inletfitting opening to said inner chamber and adapted for connection to saidfuel reservoir and a purge fitting opening from said annular chamber andadapted for connection to said induction system, a quantity of fuelvapor adsorbing material contained in the portion of said body memberimmediately below said annular end wall grid and said inner grid andsurrounding the portion of said inner wall below said end wall, a finemesh nylon screen underlying said adsoRbing material, a molded plasticlower wall member underlying and supporting said screen and saidadsorbing material, said lower wall member being molded in a griddefining a plurality of apertures therethrough, said lower wall memberhaving a depending skirt biased into engagement with said side wall, alower filter pad underlying said lower wall member grid, a moldedplastic base member secured to the lower end of said side wall, saidbase member having an annular shoulder extending inwardly from said sidewall and defining a central opening and having a bar extendingdiametrically across said opening to divide said opening into twoportions, said shoulder and said bar supporting said lower filter pad,and a wave spring member supported on said shoulder and biasing saidlower wall member upwardly against said adsorbing material to retainsaid material in a tightly packed condition.
 13. A canister for use in asystem for controlling loss of fuel vapor from a vehicle having a fuelreservoir and an internal combustion engine with an induction passage,said canister comprising a molded plastic body member having a generallycylindrical side wall with a vertical axis, an annular end wallintersecting said side wall at its upper end and extending inwardlytherefrom, said end wall being molded in a grid defining a plurality ofapertures extending therethrough, said end wall having an upwardlyextending sealing lip circumscribing said grid, an upwardly openinggenerally frusto-conical inner wall disposed concentrically about saidaxis and intersecting said end wall and extending upwardly anddownwardly therefrom, and an inner grid disposed at the lower end ofsaid inner wall, said inner grid defining a plurality of aperturesextending therethrough, a molded plastic cover member secured over saidbody member and engaging said sealing lip and said inner wall to definean annular chamber above said annular end wall grid and an inner chamberabove said inner grid, said cover member having an inlet fitting openingto said inner chamber and adapted for connection to said fuel reservoirand a purge fitting opening from said annular chamber and adapted froconnection to said induction system, a quantity of fuel vapor adsorbingmaterial contained in the portion of said body member below said annularend wall grid and said inner grid and surrounding the portion of saidinner wall below said end wall, a molded plastic lower wall memberunderlying and supporting said adsorbing material, said lower wallmember secured to said side wall and being molded in a grid defining aplurality of apertures therethrough, a compressed annular polyurethanefilter pad disposed between said annular end wall grid and saidadsorbing material, a compressed inner polyurethane filter pad disposedbetween said inner grid and said adsorbing material, a compressed lowerpolyurethane pad disposed between said adsorbing material and said lowerwall member, the compression of said polyurethane pads retaining saidadsorbing material in a tightly packed manner, an air filter padunderlying said lower wall member grid, and a molded plastic base membersecured to the lower end of said side wall, said base member having anannular shoulder extending inwardly from said side wall and defining acentral opening and having a bar extending diametrically across saidopening to divide said opening into two portions, said shoulder and saidbar supporting said air filter pad.